function get_request(){
  xhr=new XMLHttpRequest();
  xhr.onreadystatechange=function(){
        if(xhr.readyState==4 && xhr.status==200){
            call_back(xhr);
        }

    }
    xhr.open("GET","ajax_request",true);
    xhr.send(null);
}
function call_back(xhr){
   var myObject=JSON.parse(xhr.responseText);
   alert('xhr message:'+myObject.message);
}

